Currently, a user usually connects a mobile device (such as a mobile phone or a tablet computer) to an external power supply by using a charging device (such as a charger), so as to implement charging of the mobile device; or a user connects a mobile device to an external device by using a universal serial bus USB port, which can also implement data exchange between the mobile device and the external device or implement charging of the mobile device.
Current charging circuits cluster on a side of a mobile device; therefore, as calculated according to highest conversion efficiency 93% of a charging circuit in a current ideal situation, a charging circuit on the side of the mobile device generates a heat loss of 0.7 W, which causes a heat generation problem during a process of charging the mobile device, thereby bringing discomfort to a user in use.
In addition, with rapid development of mobile devices, battery capacities of the mobile devices are increasing, and a shorter charging time is required. If a conventional charging circuit continues to be used for charging a mobile device, a charging time is excessively long. Therefore, a USB power supply standard is added to a latest USB standard, a supply voltage is increased to 20 V, and a supply current is increased to 5 A, so as to quickly charge a mobile device in a short time. However, because of a significant increase in the supply voltage and the supply current, a heat generation problem during a process of charging the mobile device is more serious. When a current of 5 A is provided for a mobile device according to a latest USB power supply standard, a charging circuit on the side of the mobile device generates a heat loss of 7 W, and this heat loss cannot be endured by a current mobile device.
To resolve a current heat generation problem during a process of charging a mobile device, and to make the mobile device adapt to a charging mode in which an a supply voltage and a supply current have been increased, cooling measures such as graphite attaching or air cooling is used on the side of the mobile device, so as to reduce a heat loss generated during the process of charging the mobile device. However, in this method, a volume of the mobile device is increased, and when a charging current keeps increasing, the heat loss of the mobile device cannot be reduced radically, which are limitations of the prior art.